1. Field of the Invention
The present invention relates to communication systems. More specifically, the present invention is directed to a data communication system enabling a central station to communicate with remote stations by identifying and addressing remote stations having data to send to the central station.
2. Description of the Prior Art
In a conventional communication system a plurality of remote stations are located in consecutive positions in a serial arrangement on a data highway with a central station requesting a reply from each remote station desiring to use the data highway. In order to receive data from the remote stations, the central station is arranged to send a coded request to each remote station. Upon receipt of the coded request, a remote station identified by the particular request code being transmitted will respond with a data signal on the data highway if the remote station has data to transmit to the central station. In order to identify the remote stations issuing reply data signals on the data highway, the reply data signals are coded to correlate the remote station with the data being supplied for use by the central station. Such a prior art system requires the serial interrogation of each remote station by the central station whether or not the remote station being interrogated has data to transmit to the central station. This interrogation is wasteful of the use of the data highway as well as the time alloted for servicing of the remote stations.